Problem: Which of the following numbers is a factor of 195? ${2,4,7,10,13}$
Explanation: By definition, a factor of a number will divide evenly into that number. We can start by dividing $195$ by each of our answer choices. $195 \div 2 = 97\text{ R }1$ $195 \div 4 = 48\text{ R }3$ $195 \div 7 = 27\text{ R }6$ $195 \div 10 = 19\text{ R }5$ $195 \div 13 = 15$ The only answer choice that divides into $195$ with no remainder is $13$ $ 15$ $13$ $195$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $13$ are contained within the prime factors of $195$ $195 = 3\times5\times13 13 = 13$ Therefore the only factor of $195$ out of our choices is $13$. We can say that $195$ is divisible by $13$.